1. Field of the Invention
The present invention relates in general to a process for automatically controlling construction equipment such as power excavators to conduct the desired operations.
2. Description of the prior Art
As well known to those skilled in the art, the working members such as a boom, an arm and a bucket of a typical power excavator are designed to be operated by pressurized oil outputted from a hydraulic pump driven by an engine. In typical power excavators, the pressurized oil of the pump is delivered to working member's actuators such as a boom cylinder, an arm cylinder and a bucket cylinder under the control of directional control valves. Therefore, starting, stopping and moving the working members or the actuators can be controlled by controlling the above directional control valves.
In addition, automatic power excavator have been proposed and used. The above automatic power excavator is provided with a control system for automatically controlling the operation of the actuators. The automatic control system typically includes a controller such as a microprocessor used for processing a preset control program. The above control system also includes a plurality of electrical control levers for applying the lever signals to the controller and for setting target values of the working members. The control system further includes a plurality of positional sensors for sensing output values, that is, the operational positions and angles of the working members, and for applying output value signals to the controller.
FIGS. 1 and 2 are block diagrams representing the construction and operation of the typical automatic control system for the automatic power excavator. The power excavator with the control system of the above drawings is assumed to have four working members, that is, a swing motor, a boom, an arm and a bucket.
As shown In FIG. 1, a plurality of signal sets "sa", "sb", "sc", "sd" and "se" flow in the control system when automatically controlling the operation of the four working members. Each signal set "sa", "sb", "sc", "sd", "se" has four signals used for controlling the four working members, respectively. The output value signals "se" outputted from the positional sensors mounted to the working members are fed back to the controller. Upon receiving the output value signals "se", the controller operates, i.e., processes the above signals "se" in accordance with the preset control program and applies the control signals "sa" to the directional control valves. At this time, the operator of the excavator presets the above control program by operating the control panel of the dashboard prior to starting the control system. In the operation of the power excavator, the operator starts or stops the working members or controls the moving directions of the working members by handling the electrical control levers. The control system will automatically be operated after starting in the manner as shown in FIG. 2. That is, the control system is almost automatically operated after starting under the control of the controller, while the operator simply handles the electrical control levers to perform as the above-mentioned extremely limited part, i.e., start or stop the working members or control the moving directions of the working members.
Typically, power excavators conduct various types of operations, such as land finishing and loading operations, under various working conditions. That is, power excavators may be operated on either rugged or smooth sites. Power excavators may be operated on sites having many or no obstacles. The weather of the sites may also vary. In addition, the power excavators may be operated on either firm or soft ground. However, the typical control programs used with the automatic control systems for the power excavators are programmed to be used in extremely normal working conditions. That is, the typical control programs are not programmed considering the different working conditions of the excavators due to technical difficulties. In this regard, when an automatic power excavator is operated in an abnormal working condition, for example, a rugged site having many obstacles, the power excavator will not achieve the desired operational precision. The power excavator in the above state will also be faced with the danger of a rollover accident.
As described above, the operator of the above automatic control system simply handles the electrical control levers to perform the extremely limited part, while the control system is almost automatically operated after starting under the control of the controller. Therefore, the automatic power excavator cannot be optimally operated in the abnormal working conditions, particularly, on a rugged site having many obstacles. In addition, the control algorithm of the control system for conducting a series of operations is extremely complicated. In order to conduct a series of operations under the control of the control system, the output values, or the output positions and angles of the working members, are sensed by positional sensors mounted to the working members. The sensors In turn apply output value signals to the controller. Upon receiving the output value signals, the controller operates,i.e., processes, the output value signals while comparing the output values with the preset target values, thereby precisely determining the output positions and angles of the working members. The controller in turn outputs control signals to the directional control valves, thereby allowing the working members to achieve the target positions and angles. The above control process overloads the controller and thereby extremely complicates the control algorithm. In this regard, the control process not only increases the cost of the control system, it also prevents the automatic power excavators from being optimally used in poor working conditions. The above control process also reduces the operational precision of the power excavators which operate in poor working conditions. The above problems are caused by the fact that the positional sensors mounted to the working members only sense the rudimentary output values of the working members. Furthermore, the controller only roughly controls the control system in accordance with the preset control program without any regard for the working conditions of the power excavator.
The automatic control system for the power excavators may be provided with many more sensors in order to optimize the control performance of the control system. However, the sensors are not only apt to experience difficulties in the poor working conditions, they also increase the cost of the control system.
In the above control process, the operator is required to handle the electrical control levers every time the operation of the power excavator changes to another operation. Therefore, the control process fails to preferably improve the operational efficiency of the excavator and is still inconvenient to the operator. Another problem of the above control process is resided in that the operator should handle the control levers when the operation of the power excavator needs to be slightly changed.